1. Field of Invention
The invention relates to the apparatus and methods for chemical vapor deposition (CVD). The invention further relates to the planetary form of susceptor rotation utilized in CVD.
2. Description of Prior Art
In prior-art apparatus and methods for CVD, the primary emphasis has been on producing uniform layers of coating, see for example U.S. Pat. No. 5,455,070 by Anderson, U.S. Pat. No. 5,455,069 by Lee, U.S. Pat. No. 5,173,336 by Kennedy, U.S. Pat. No. 4,976,996 by Monkowski, or U.S. Pat. No. 4,705,700 by Ikeda. For simultaneously coating multiple substrates in batch processing, the planetary form of susceptor rotation is utilized extensively to achieve the level of coating uniformity required over each substrate and from substrate to substrate within a batch, see for example U.S. Pat. Nos. 4,961,399 and 4,860,687 by Frijlink, or U.S. Pat. No. 3,424,628 by Winings. FIG. 1 illustrates one example of the prior-art planetary form of susceptor rotation, where a main susceptor 14 rotates at a rotation rate of .omega..sub.m in the indicated direction about main axis 20 and includes a number of secondary susceptors 114, 214, and 314. Secondary susceptors 114, 214, and 314 rotate at the same rotation rate .omega..sub.s in the indicated direction about secondary axes 120, 220, and 320 respectively. Excellent coating uniformity within a batch, including uniformity over each substrate and from substrate to substrate, has been achieved using this prior-art planetary form of susceptor rotation.
The prior-art apparatus and methods for CVD with planetary susceptor rotation as described are sufficient to achieve the required coating uniformity over each substrate in a batch once the process for a specific coating is developed for production. However, during the process development for a specific coating, applying the prior-art apparatus and methods results in wasted source materials and unnecessary development time and cost. The prior-art apparatus for CVD with planetary susceptor rotation consumes the same amount of source materials whether one test substrate is being coated for process development or multiple substrates are being coated for production. Multiple iterations of process corrections are required to achieve the proper layer thicknesses and/or compositions during the development of a specific coating process. Each additional iteration requires a separate batch of substrates to be coated and further increases the development time and cost.